The present invention relates generally to helmet construction and, more particularly, to a new and improved protective helmet for use primarily by persons engaged in sporting or other activities exposed to the risk of head injury.
Helmets. Helmets used by bicyclists and others engaged in sports typically have a hard outer shell that covers energy-absorbing material. Bicycle helmets typically have a hard plastic outer shell that covers expanded polystyrene. Polystyrene absorbs energy by developing multiple micro-fractures throughout its structure. Once a polystyrene helmet develops micro-fractures it ceases to provide impact protection (i.e., such helmets are unusable after a single impact). Football helmets typically have a dense polyethylene outer shell that covers polypropylene pads capable of absorbing multiple impacts. Other helmets, such as those used by soldiers, typically have a metal or composite shell; that is able to protect a soldier""s head from certain types of high-energy impacts.
Helmets typically have a retention system to secure the helmet in proper position on the user""s head. The straps commonly used for bicycle helmets are difficult to adjust, resulting in many bicyclists wearing helmets improperly positioned and providing limited protection.
The helmet shape and the extent to which it covers the head are important design considerations. Helmets are shaped differently depending on the use to which the helmet is to be put and the energy level of the impacts the user might experience. Bicycle helmets are typically designed to protect the top, sides and front of the user""s head.
Performance standards have been developed for certain types of helmets. For bicycle helmets, for example, the Snell B-95 Bicycle Helmet Standard involves a series of performance tests. A helmet passes the impact portion of the Snell test if it prevents a head from decelerating at a rate in excess of 300 G""s when subjected to a specific test impact. The Snell 300 G""s standard does not assure that a rider wearing a helmet meeting that standard will not suffer serious head injury. Head and brain injuries occur at deceleration levels well below 300 G""s; also, riders can experience impacts that result in head deceleration levels above 300 G""s.
Head Injury. The head can be thought of as having three components: the skull; the brain, which consists of compressible matter; and the fluid filling the skull and in which the brain floats. Neither the skull nor the fluid is compressible; the brain, however, is compressible and, when forced against the skull, does compress, bruising brain tissue and perhaps causing hemorrhaging. When the skull experiences an impact, the force is transmitted through the skull and fluid; the inertia of the fluid results in the brain moving in a direction opposite from that of the force applied to the skull. If that force is applied suddenly (i.e., there is an impact) and is substantial enough, the brain moves through the fluid and strikes the inside of the skull at a point roughly opposite to the area of the skull that sustains the impact.
When the brain strikes the skull with moderate force, the brain tissue in the area of the brain that hits the skull is compressed and bruised. That typically results in a temporary cessation of nervous function (i.e., a concussion).
When the skull is subjected to a more substantial impact, the brain typically hits the inside of the skull at a higher speed; a larger area of brain tissue is compressed and damaged and brain hemorrhaging is common (i.e., contusion results). If minimal hemorrhaging occurs, the individual may experience symptoms similar to those of a concussion. More substantial hemorrhaging may result in a loss of blood supply to the brain and even death.
When the energy level of the impact to the skull is substantial enough, the skull fractures. When it does, some of the impact energy is dissipated. A fracture may be either linear or localized. A linear fracture, the simpler of the two, is essentially a straight line crack. A localized fracture is one in which multiple fractures occur in a single area. In such a fracture, it is common for skull bone material to be displaced; the displacement can result in bone material penetrating brain tissue, causing hemorrhaging and swelling.
Research Considerations. We concluded it would be desirable to design a helmet that achieved the lowest possible rate of deceleration and thus maximum protection for the head. Published research suggests that the human skull can fracture at decelerations as low as 225 G""s and that concussions can occur at substantially lower decelerations.
Published research showing that most helmet impacts experienced by bicyclists occurred at the right and left temporal areas of the head aided us in product design. Other research aided us in designing our tests and in identifying materials worthy of consideration.
One object of the present invention is to provide a helmet having multiple foam layers for reducing the deceleration experienced by the head.
Another object of the present invention is to provide a new, improved protective helmet that will, under the testing criteria employed, prevent a head from decelerating at a rate in excess of 100 G""s.
Yet another object is to provide a helmet arrangement that can withstand multiple impacts and still be reusable.
Still a further object is to provide a new, improved protective helmet that can be easily and efficiently manufactured and marketed.
Another object is to provide a new, improved protective helmet of a durable and reliable construction.
Yet another object is to provide a protective helmet that can be manufactured at an economically acceptable cost to the buying public.
The present invention can be characterized in a variety of ways. In one characterization, the helmet is comprised of a relatively stiff outer shell and a plurality of impact-energy-absorbing material layers disposed within the outer shell in juxtaposition to each other. At least one of these impact-energy-absorbing material layers is made of an open-celled polyurethane foam.
The invention may also be characterized as a helmet comprising a relatively stiff outer shell and a plurality of impact-energy-absorbing material layers disposed within the outer shell in juxtaposed position to each other. The impact-energy-absorbing material layers, in combination with the relatively stiff outer shell, are selected so that the helmet will prevent a head from decelerating at a rate in excess of 100 G""s under the testing criteria employed.
It is further theorized that the invention can be characterized as a helmet comprising a relatively stiff outer shell and a plurality of impact-energy-absorbing material layers disposed within the outer shell in juxtaposed position to each other. In accordance with this characterization of the invention, the material layers are selected such that they are capable of restoring to their original shape following impact and/or repeated impacts.
In a preferred embodiment, the present invention is directed to a helmet comprised of an outer shell, energy-absorbing layers, and a retention system for securing the helmet to the user""s head. Importantly, the energy-absorbing layers comprise at least a first layer of impact-energy-absorbing material adjacent to the outer shell, a second layer of impact-energy-absorbing material adjacent to the first layer, and a third layer of impact-energy-absorbing material adjacent to the second layer and to the wearer""s head.
Although the preferred embodiment is comprised of three layers of open-celled foam, it is theorized that the three layers may be replaced with four, five or more layers preferably each having lesser thickness than each layer in the three-layer embodiment to avoid construction of an unnecessarily large helmet. If four or more layers are utilized, the composite thickness preferably is the same as the thickness achieved in the three-layer design.
In the preferred embodiment, the outer shell is preferably made of PETG (glycol-modified polyethylene terephthalate), which is a copolyester plastic having excellent impact strength, durability and the ability to be thermo-formed. Preferably, but not necessarily, the outer shell has an optimal thickness of 0.02 inch.
Also in the preferred embodiment, the first of the energy-absorbing layers (i.e., the layer adjacent to the outer shell) is made of ergonomic, open-celled polyurethane foam, such as CONFOR(trademark) foam manufactured by E-A-R Specialty Composites Corporation.
In the preferred embodiment, the first layer is made of CF-40 yellow foam. The second layer is preferably made of ergonomic, open-celled polyurethane foam having a higher stiffness than the first layer. The second layer, in the preferred embodiment, is made of CF-47 green foam.
The third of the energy absorbing layers, the layer closest to the head, is preferably made of the same material as the first layer. In the preferred embodiment, therefore, the third layer preferably is also made of CF-40 yellow foam.
Each of the three energy absorbing layers is preferably about 0.5 inch thick.
The foregoing materials were selected as a result of extensive testing of and experimentation on these and other foams.
The foregoing materials were also selected because of other important characteristics they possess, such as having low-impact, high-rebound properties. These materials conform easily to different shapes, such as the shape of a wearer""s head, and are non-irritating in dermal contact.
An important feature of the invention is the multiple layering of energy-absorbing foams of different stiffnesses (some or all of the layers may or may not have the same density). The layering pattern of such foams results in a structure that reflects propagating stress waves upon impact through the materials and that ultimately enables the structure to absorb larger amounts of energy than the same individual material not layered with alternating stiffnesses. The foregoing layering pattern of the invention was selected following extensive experimentation and calculation.
The retention system preferably comprises three separate straps. The first strap is wrapped around the front of the head and attached to an occipital support. This first strap is elastic and is independent of the rest of the strapping.
The second strap is preferably looped through two holes formed in the shell and the foam layers and is pulled down over the ear in a V-shaped form. The third strap is symmetric to this strap on the other side of the helmet. Preferably, two individual straps are used, rather than a single strap. (A single strap is used in many helmets today.) Other retention systems can also be used.
An advantage of using open-celled polyurethane foam, such as the CONFOR(trademark) foam, is that it can withstand multiple impacts. The helmet of the present invention absorbs energy notwithstanding multiple impacts; it also rebounds, beneficially returning to its original shape over time. Therefore, the helmet of the present invention can be used over and over again; it does not have to be replaced after a single impact. Indeed, if in a single accident the helmet receives more than one impact, the foam""s properties, including its ability to retain shape, advantageously insure that the helmet maintains its integrity and purpose. In contrast, most helmets currently in use dissipate energy by cracking. Once such a helmet has dissipated energy it will not protect against injury and must be discarded.
The aforementioned novel use of the CONFOR(trademark) material is complimented by the further advantage that the material is soft and extremely comfortable, in contrast to the rigid expanded polystyrene commonly used today.
Although the preferred embodiment features three layers of impact-energy absorbing, open-celled polyurethane foam, the scope of the invention contemplates additional energy-impact absorbing layers as may occur to persons skilled in this art following review of the novel disclosure herein. In some circumstances, it is theorized that the objects of the invention may be achieved with two layers of open-celled polyurethane foam (e.g., CONFOR(trademark) materials), appropriately sized and dimensioned in thickness.
It is within the scope of this invention to utilize energy-absorbing layers of varying thickness and not necessarily the same thickness as in the preferred embodiment.
One or more comfort pad strips may be attached to this exposed inner surface to allow air to circulate between the helmet and head without denigrating the performance characteristics of the helmet.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, not as restrictive.